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FREQUENTLY ASKED QUESTIONS

Power Part

1.1 Is it possible to use diode to convert 5V to 4.4V for power supply?

It is not recommended to use this method, because the forward voltage of diode will change as the current changes, which will cause the instability of the module’s power supply and make the module work abnormally.It is not recommended to use this method, because the forward voltage of diode will change as the current changes, which will cause the instability of the module’s power supply and make the module work abnormally.

1.2 Is it possible to use standard USB to supply power for the module?

The output current of standard USB interface is max.500mA, which does not meet the peak current demand of GPRS module. If USB interface is required to supply power for the module, you can operate like below:

1) Use AT+QGPCLASS to set the GPRS level to 8. This command will take effect after next restart of the module. There is only one uplink slot when the GPRS level is 8.

2) Connect two 2200uF capacitors with low ESR value to VBAT pin and keep them close to the module.

3) It is recommended that the VBAT voltage should be adjusted between 4.2V and 4.5V which can prevent the module from working abnormally due to the voltage drop of VBAT.

4) Test the module under the weak signal environment (such as CSQ value is less than 14). If the module works properly, it indicates that USB interface can supply power for the module.

1.3 How to use higher DC voltage (e.g. automotive 12V/24V/48V) to power the module?

It is suggested to implement it by two stage conversion. First stage is to step down to 5V via DC-DC converter and the second stage is to convert to 4V from 5V via LDO as shown in the figure below.

1.4 How to test the power consumption in the sleep mode?

The best way to test the power consumption of module is to supply power for module separately in case that peripheral circuit might cause extra power consumption.ONLY VBAT/GND/SIM/RF/PWRKEY should be connected, in this case, the power consumption on VBAT will be the exact consumption of module.

To test the power consumption on the EVB board, please operate like below:

(1) Remove the resistor R110 and R102.

(2) Solder R224 with a 0Ω resistor.

(3) Plug the power adapter and turn on the 5V power switch. See figure below.

Note:

1. Removing R110 is to make sure that the power supply of module is directly from the external power via J103.

2. Power adapter should be plugged to offer the power for the RS232 converter and LEDs, which will avoid the increase of power consumption caused by sink current.

3. VDD_EXT of module is used to supply the power for RS232 converter. In order to avoid the RS232 converter being supplied by VDD_EXT, R102 should be removed. Meanwhile, R224 should be soldered a 0R resister to supply the power for RS232 converter with 5V power adapter.

Serial Part

2.1 How to deal with the UART communication failure?

First of all, check the level of STATUS pin to judge whether the module is powered on or not. High level means the module is on and low level means the module is off. If module has already been powered on, you need to analyze it according to the following two situations.

2.1.1 Abnormal Communication between PC and EVB

1) Check whether the serial cable is OK or not. It is recommended to use the Quectel serial cable, which can avoid the abnormal communication between PC and EVB when using three-wire serial cable under the hardware flow control.

2) Check the usage of the serial tool is right or wrong. If you use QCOM tool provided by Quectel, please tick RTS as the following figure.

2.1.2 Abnormal Communication between MCU and module

1) Please check whether the baud rate of MCU is corresponding with the module’s or not. Quectel module is set as autobauding by default. Send 2~4 AT Commands to synchronize the baud rate of the module. Some modules might need more AT commands to get synchronized. Once the module gets synchronized, it is suggested to use AT+IPR command to fix the baud rate and use AT&W to save it.

2) If using three wires to connect MCU and the module, it is needed to check if the hardware control is closed.

2.2 How to match the UART level between MCU and module?

1) If the UART level of MCU is 3.3V, the level shift circuit is shown as below.

2) If the UART level of MCU is 3V, just change the resistor value of 5.6K in the above Figure to 15K.

3) If the UART level of MCU is 5V, the level shift circuit is shown as below.

When SIM card is pulled out or plugged in, module will immediately respond:

+CPIN:NOT READY

+QSIMSTAT:1,0 or +QSIMSTAT:1,1

Call Ready

3.2 SIM card cannot be recognized after the module works for a while.

Description: module responds +CPIN: READY after powering on, but after a while, it responds +CPIN: NOT READY. You can analyze the issue from the following aspects.

1) RF interference

a. You can use AT+CFUN=4,1 to disable the RF function and check if the issue still exists.

b. Put the antenna close to the SIM card and SIM card signal line to check if the issue appears more frequently.

c. Please check if there is electrical/magnetic field around the testing field, for example, high voltage transmission lines, high-power wireless devices, etc. Try to use shielding case to cover the SIM card and all the SIM signal lines to confirm if the issue will be resolved.

If the VBAT trace is too close to the SIM card signal line, module can still recognize the SIM card because of the low ripple of VBAT when powering on. But when module starts to register to the network, the ripple will become higher and interfere the SIM card signal line, which might cause the module not to recognize the SIM card. You can cut off the power supplied to the module and use external power source to directly feed to VBAT pin of module to see if the issue is resolved.

3) Poor quality of SIM card

a. Change another SIM card to see if there is the same problem on the new SIM card.

b. Put the problematic card on the Quectel EVB or cell phone to see if there is the same problem.

3.3 What reasons can cause the module not to register to the network after powering on?

1. Use AT+CPIN to check whether module can recognize the SIM card or not.

2. Check whether the SIM card is out of service or not.

3. Use AT+QBAND and AT+CFUN to check the working band and working mode of the module respectively.

4. Use AT+CSQ to check whether the RF signal is normal or not.

5. Use AT+GSN to check whether the IMEI number of the module is legal or not. Some customers may change the IMEI number, which causes network in some areas to regard this changed IMEI number as illegal and forbid the module to register to the network.

Call Part

4.1 How to set the caller ID and the Connected Line Identification Presentation (CLIP)?

1. You can use AT+CLIP=1 to present the calling line. And you can set AT+QCLIP=1 to present the string type corresponding to the entry saved in the phone book.

2. You can use AT+COLP=1 to present the connected line. And you can set AT+QCOLP=1 to present the string type corresponding to the entry saved in the phone book.

Example:

AT+CPBW=1,"02151082965",129,"QUECTEL" //write phonebook entry

OK

AT+QCLIP=1 // present the string type corresponding to the entry saved in the phonebook

4.2 What is the maximum time that the module responds OK after executing ATH to hang off a call?

According to the 3GPP standard, the maximum time that the module responds OK after executing ATH to hang off a call is 90seconds. You can set the proper timeout of ATH in the MCU program based on the maximum time.

PHB Part

5.1 How to configure and query subscriber number?

AT+CPBS="ON" //choose “ON” type of phonebook

AT+CPBW=1,"number" //write subscriber number

AT+CNUM //query subscriber number

5.2 How to configure/query phonebook number?

AT+CPBS="SM" //choose “SM” type of phone book, which is to operate the phonebook saved in SIM card

6.3 How many methods of receiving data under TCP/UDP connection?

B. Buffer access mode: Read received data from internal buffer using AT commands.

2. Transparent mode:

You can only get received data directly from the UART port in this mode.

6.4 What is the maximum length of data sent by AT+QISEND?

1460 bytes.

6.5 What is the maximum value of the parameters returned by AT+QISACK?

Each parameter returned by AT+QISACK is defined as 32 bits data in the TCP protocol, so the maximum value of the parameters is 2^32 = 4294967296byte.

6.6 Why the server has not yet received the data after the module responds “SEND OK”?

When module receives “SEND OK”, it only means the data has already been sent to the buffer of the TCP socket rather than sent to the server. You can use AT+QISACK to check whether the data has been sent to the server or not.

6.7 In which cases will module respond CLOSED?

Module will respond CLOSED in the following three conditions:

1. TCP connection is closed by the server.

2. If module still cannot receive ACK from server after re-trying to transmit data to the server for 12 times, it will automatically close TCP connection and respond CLOSED.

3. TCP connection might be interrupted and module will respond CLOSED due to the abnormality of network.

6.8 What is the difference between CGDCONT and QICSGP?

When using module’s embedded stacks like TCP and UDP protocol, you need to use AT+QICSGP to configure the APN. While using PPP, you need to use AT+CGDCONT to configure the APN.

RF Part

7.1 What are the design considerations when using embedded antenna?

1. Choose DC-DC converter with low switching frequency.

2. The input and output line of DC-DC converter should be far away from antenna. Note: All Power Supplies should be far away from antenna.

3. Antenna should be far away from LCD, especially the FPC of LCD.

4. Antenna and RF trace should be far away from the main CPU, including the SDRAM and FLASH. It is recommended to add EMI filters at the high-speed line of CPU, SDRAM and FLASH.

5. Use the shielding case to cover the CPU, SDRAM, FLASH and DC-DC converter.

6. Antenna should be far away from the SIM card.

7. Please ensure that the enclosure surrounding the antenna and structural components are not metal materials.

8. As the enclosure and components surrounding the embedded antenna will have influence on the RF performance, it is strongly suggested to provide the device to the antenna vendor to optimize the antenna performance. Also Quectel provides the document <Antenna_Design_Notes> for your reference.

7.2 Can the RF pin endure thunder stroke?

There is TVS inside module which is only to prevent ESD. If the device is required to endure thunder stroke , you can connect a professional anti-lightning TVS to the RF_IN pin outside of module and make sure that the capacitance of TVS should be lower than 0.5pF.

7.3 What is the impact if many modules work simultaneously and the antennas of modules are very close to each other?

1. If the antennas of modules are too close to each other, it will bring EMI interference within the antennas, which will result in the decline in the signal quality and the raise of BER, and cause long time connection or connection failure issue. It is suggested that the distance between each antenna should be more than 20cm.

2. If many modules are working simultaneously, it could cause some modules unable to register to network due to lack of base station resources. It is recommended to use QuecScan/QuecLock function to lock different modules at different frequencies. For Details, you can refer to <GSM_QuecCell_AT_Commands_Manual>. Also, you can use SIM cards of different operators if possible.

7.4 What is the maximum transmitting speed of GPRS?

The uplink and downlink time slots will be 4 in GPRS CLASS 12. Using CS4 coding method it is possible to achieve a user speed of maximum 85.6Kbps. (For Details, please refer to below chart.)

Note: The actual speed depends on the network status. For example, the actual average speed tested in Shanghai is 30kbps.

Audio Part

8.1 What is the audio output capability of the module?

Module can drive a maximum 8ohm load resistance if there is an embedded AB amplifier inside it. If there is no embedded AB amplifier in the module, then module can drive a maximum 32ohm load resistance. It is needed to add an external audio amplifier to drive 8ohm load resistance.

8.2 What could be the reason why the call somehow hangs off when you use ATD to make a call?

1. Check if MCU sends ATH command to close the call.

2. Check whether there are capacitors with high capacitance like more than 1uF in the audio interface. In general，only 10pf and 33pf capacitor can be connected to the audio interface to eliminate the RF interference. Capacitor with high capacitance will cause the instability of audio PA, which may lead to the call hanged off.

SMS Part

9.1 What are the differences between text mode and PDU mode?

There are two modes for SMS, Text mode and PDU mode.

1. When using text mode, it is needed to configure some parameters via AT commands like AT+CMGF, AT+CSCS and AT+CSMP.

2. When using PDU mode, you need to include all of the parameters like MS center number, receiver’s number and the validity into one PDU string.

9.2 What is the maximum individual short message size?

According to the 3GPP standard, the maximum individual short message size is 1120bits. When using different coding scheme, the maximum individual short message size could be different. Please see details as below:

9.3 What is long SMS?

Long message is composed of multiple SMS messages. The long message will be split into multiple short messages and sent out. The receiving terminal is then responsible for reassembling the short messages and presenting them to the user as one long message. Each short message will start with aTP-UDH1 containing segmentation information (TP-UDH1 is set as 1). For Quectel modules, long message can contain maximum 7 short messages.

9.4 How to deal with the incoming message when SMS memory space is full?

When SMS memory space is full, the incoming message cannot be received.

Module will respond error when sending some SMS commands if SIM card initialization is not finished, so it is necessary to finish the SIM card initialization before operating SMS commands. In general, SIM card initialization will be finished in about 20s after powering on. However, for some SIM cards, it will take about 40s to finish the initialization due to different electrical characteristics. You can use AT+QINISTAT to check the status of SMS initialization. +QINISTAT:3 means the SMS initialization is finished and then you can operate the SMS commands.

Note: Before SIM card initialization is finished, executing the following commands will respond error.

PPP Part

10.1 How to use PPP to dial up in the WIN7 OS?

1. Choose “network and sharing centre” in the control panel.
2. Choose “set a new connection and network” in the “network and sharing centre”.
3. Choose “set dial up connection” in the “set a new connection and network”.
4. Choose “skip” in the following interface.
5. Choose “change the adapter configuration”.
6. Choose “attribution”, choose 115200 baud rate in the general option and then click “OK”.
7. Choose “dial up”, then finish the PPP dial up.

10.2 What are the possible reasons for the failure of PPP dial up?

1. Does the serial port be occupied by other serial communication tools when dialing?
2. Are the baud rate of module, modem and dial up the same?
3. Is the APN configuration right or wrong in the modem?
4. Is the device five-wire designed or three-wire designed? Does the device open or close the hardware flow control?
5. Is the tested SIM card being PIN locked? Is SIM card in arrearage?

MMS Part

11.1 Can UTF8 and UCS2 coding scheme be supported in the MMS? Which one is better?

Both UTF8 and UCS2 are supported. However, it is recommended to use UTF8 coding scheme because the network compatibility for UCS2 coding scheme is not so good.

FLASH Part

12.1 What is the lifetime of the module flash?

The erasable lifetime of various flashes is about 100,000. In order to extend the lifetime of flash, we adopted the dynamic reading and writing technology in our modules. With this technology, we can write the data to each section of the flash instead of the same block, which will avoid the damage to the flash chipset. So each section in the flash will have the same chance to be used, which in turn extends the lifetime of the flash.

Customer Service & Support

For any questions or cooperation issues, please contact our sales, FAE and marketing team freely.